Basing in studies which have related the darunavir (DRV) virtual inhibitory quotient (vIQ) with the virological response, it is possible to think in the possibility of simplifying the rescue treatment with DRV/ritonavir to 900/100 mg once a day in those patients who are being treated with DRV/ritonavir 600/100 mg twice a day and who, besides having undetectable viral load, have a vIQ over 2. This strategy would not jeopardize the efficacy of the antiretroviral treatment and would have less impact in the lipid profile of the patients as well as less pharmaceutical expenditure.

The probability of achieving viral replication suppression during the treatment with DRV has been related to both the extent of viral resistance to DRV (inhibitory concentration 50%, IC50) and the drug concentration. Moreover, the DRV virtual inhibitory quotient (vIQ) has been related significantly with the virological response to DRV treatment. So patients with a DRV vIQ >= 1,5 had a 8-times higher probability of having viral load < 50 copies/mL after 24 weeks of treatment than those having a vIQ < 1,5.

Considering the previous arguments, it is possible to think in the possibility of simplifying the rescue treatment with DRV/ritonavir to 900/100 mg once a day in those patients who are being treated with DRV/ritonavir 600/100 mg twice a day and who, besides having undetectable viral load, have a DRV vIQ over 2. This strategy would not jeopardize the efficacy of the antiretroviral treatment and would have less impact in the lipid profile of the patients as well as less pharmaceutical expenditure.

In women, negative pregnancy test or not in fertile age (defined as at least one year from menopause or undergoing any surgical sterilisation technique), or undertaking to use a barrier contraceptive method during the study.

Signature of the informed consent.

Exclusion Criteria:

AIDS-defining illness in the last 4 weeks.

Suspicion of unsuitable antiretroviral treatment compliance.

In women, pregnancy or breastfeeding.

Record or suspicion of incapability to cooperate as appropriate.

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Please refer to this study by its ClinicalTrials.gov identifier: NCT00611039